Image courtesy E.V. Masongsong/UCLA

ScienceShot: Powering Up the Magnetosphere

Taking advantage of a rare chance alignment of eight Earth-orbiting spacecraft, space physicists have pinned down where and how the energy of the solar wind can surge Earthward to power the celestial light of the auroras and help fire up the Van Allen radiation belts. Researchers knew that the magnetosphere—Earth’s magnetic bubble of plasma—gets its energy from solar wind, which blows the plasma into its teardrop shape and stores energy by stretching and compressing the magnetosphere’s magnetic field lines (blue). These stressed magnetic field lines can merge, or reconnect, at a point about halfway between Earth and the orbit of the moon. But, contrary to expectations, the stored energy is not just released where reconnection occurs, researchers report online today in Science. Instead, energy is released at a magnetically intense “front” as reconnection slings the front toward Earth at almost 1.5 million kilometers per hour (and sends another front toward deep space). The passage of a front heats the plasma (yellow zone) and sends charged particles flying toward Earth (red arrow), where the onslaught powers both radiation belts and aurora.

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